Kernel Parameters ~~~~~~~~~~~~~~~~~ The following is a consolidated list of the kernel parameters as implemented (mostly) by the __setup() macro and sorted into English Dictionary order (defined as ignoring all punctuation and sorting digits before letters in a case insensitive manner), and with descriptions where known. Module parameters for loadable modules are specified only as the parameter name with optional '=' and value as appropriate, such as: modprobe usbcore blinkenlights=1 Module parameters for modules that are built into the kernel image are specified on the kernel command line with the module name plus '.' plus parameter name, with '=' and value if appropriate, such as: usbcore.blinkenlights=1 This document may not be entirely up to date and comprehensive. The command "modinfo -p ${modulename}" shows a current list of all parameters of a loadable module. Loadable modules, after being loaded into the running kernel, also reveal their parameters in /sys/module/${modulename}/parameters/. Some of these parameters may be changed at runtime by the command "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}". The parameters listed below are only valid if certain kernel build options were enabled and if respective hardware is present. The text in square brackets at the beginning of each description states the restrictions within which a parameter is applicable: ACPI ACPI support is enabled. ALSA ALSA sound support is enabled. APIC APIC support is enabled. APM Advanced Power Management support is enabled. AX25 Appropriate AX.25 support is enabled. CD Appropriate CD support is enabled. DRM Direct Rendering Management support is enabled. EDD BIOS Enhanced Disk Drive Services (EDD) is enabled EFI EFI Partitioning (GPT) is enabled EIDE EIDE/ATAPI support is enabled. FB The frame buffer device is enabled. HW Appropriate hardware is enabled. IA-32 IA-32 aka i386 architecture is enabled. IA-64 IA-64 architecture is enabled. IOSCHED More than one I/O scheduler is enabled. IP_PNP IP DHCP, BOOTP, or RARP is enabled. ISAPNP ISA PnP code is enabled. ISDN Appropriate ISDN support is enabled. JOY Appropriate joystick support is enabled. LP Printer support is enabled. LOOP Loopback device support is enabled. M68k M68k architecture is enabled. These options have more detailed description inside of Documentation/m68k/kernel-options.txt. MCA MCA bus support is enabled. MDA MDA console support is enabled. MOUSE Appropriate mouse support is enabled. MSI Message Signaled Interrupts (PCI). MTD MTD support is enabled. NET Appropriate network support is enabled. NUMA NUMA support is enabled. GENERIC_TIME The generic timeofday code is enabled. NFS Appropriate NFS support is enabled. OSS OSS sound support is enabled. PARIDE The ParIDE subsystem is enabled. PARISC The PA-RISC architecture is enabled. PCI PCI bus support is enabled. PCMCIA The PCMCIA subsystem is enabled. PNP Plug & Play support is enabled. PPC PowerPC architecture is enabled. PPT Parallel port support is enabled. PS2 Appropriate PS/2 support is enabled. RAM RAM disk support is enabled. S390 S390 architecture is enabled. SCSI Appropriate SCSI support is enabled. A lot of drivers has their options described inside of Documentation/scsi/. SELINUX SELinux support is enabled. SERIAL Serial support is enabled. SMP The kernel is an SMP kernel. SPARC Sparc architecture is enabled. SWSUSP Software suspend is enabled. TS Appropriate touchscreen support is enabled. USB USB support is enabled. USBHID USB Human Interface Device support is enabled. V4L Video For Linux support is enabled. VGA The VGA console has been enabled. VT Virtual terminal support is enabled. WDT Watchdog support is enabled. XT IBM PC/XT MFM hard disk support is enabled. X86-64 X86-64 architecture is enabled. More X86-64 boot options can be found in Documentation/x86_64/boot-options.txt . In addition, the following text indicates that the option: BUGS= Relates to possible processor bugs on the said processor. KNL Is a kernel start-up parameter. BOOT Is a boot loader parameter. Parameters denoted with BOOT are actually interpreted by the boot loader, and have no meaning to the kernel directly. Do not modify the syntax of boot loader parameters without extreme need or coordination with . Note that ALL kernel parameters listed below are CASE SENSITIVE, and that a trailing = on the name of any parameter states that that parameter will be entered as an environment variable, whereas its absence indicates that it will appear as a kernel argument readable via /proc/cmdline by programs running once the system is up. The number of kernel parameters is not limited, but the length of the complete command line (parameters including spaces etc.) is limited to a fixed number of characters. This limit depends on the architecture and is between 256 and 4096 characters. It is defined in the file ./include/asm/setup.h as COMMAND_LINE_SIZE. 53c7xx= [HW,SCSI] Amiga SCSI controllers See header of drivers/scsi/53c7xx.c. See also Documentation/scsi/ncr53c7xx.txt. acpi= [HW,ACPI] Advanced Configuration and Power Interface Format: { force | off | ht | strict | noirq } force -- enable ACPI if default was off off -- disable ACPI if default was on noirq -- do not use ACPI for IRQ routing ht -- run only enough ACPI to enable Hyper Threading strict -- Be less tolerant of platforms that are not strictly ACPI specification compliant. See also Documentation/pm.txt, pci=noacpi acpi_sleep= [HW,ACPI] Sleep options Format: { s3_bios, s3_mode } See Documentation/power/video.txt acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode Format: { level | edge | high | low } acpi_irq_balance [HW,ACPI] ACPI will balance active IRQs default in APIC mode acpi_irq_nobalance [HW,ACPI] ACPI will not move active IRQs (default) default in PIC mode acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for use by PCI Format: ,... acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA Format: ,... acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS Format: To spoof as Windows 98: ="Microsoft Windows" acpi_osi= [HW,ACPI] empty param disables _OSI acpi_serialize [HW,ACPI] force serialization of AML methods acpi_skip_timer_override [HW,ACPI] Recognize and ignore IRQ0/pin2 Interrupt Override. For broken nForce2 BIOS resulting in XT-PIC timer. acpi_use_timer_override [HW,ACPI} Use timer override. For some broken Nvidia NF5 boards that require a timer override, but don't have HPET acpi_dbg_layer= [HW,ACPI] Format: Each bit of the indicates an ACPI debug layer, 1: enable, 0: disable. It is useful for boot time debugging. After system has booted up, it can be set via /proc/acpi/debug_layer. acpi_dbg_level= [HW,ACPI] Format: Each bit of the indicates an ACPI debug level, 1: enable, 0: disable. It is useful for boot time debugging. After system has booted up, it can be set via /proc/acpi/debug_level. acpi_fake_ecdt [HW,ACPI] Workaround failure due to BIOS lacking ECDT acpi_generic_hotkey [HW,ACPI] Allow consolidated generic hotkey driver to override platform specific driver. See also Documentation/acpi-hotkey.txt. acpi_pm_good [IA-32,X86-64] Override the pmtimer bug detection: force the kernel to assume that this machine's pmtimer latches its value and always returns good values. enable_timer_pin_1 [i386,x86-64] Enable PIN 1 of APIC timer Can be useful to work around chipset bugs (in particular on some ATI chipsets). The kernel tries to set a reasonable default. disable_timer_pin_1 [i386,x86-64] Disable PIN 1 of APIC timer Can be useful to work around chipset bugs. ad1816= [HW,OSS] Format: ,,, See also Documentation/sound/oss/AD1816. ad1848= [HW,OSS] Format: ,,,, adlib= [HW,OSS] Format: advansys= [HW,SCSI] See header of drivers/scsi/advansys.c. advwdt= [HW,WDT] Advantech WDT Format: , aedsp16= [HW,OSS] Audio Excel DSP 16 Format: ,,,,, See also header of sound/oss/aedsp16.c. aha152x= [HW,SCSI] See Documentation/scsi/aha152x.txt. aha1542= [HW,SCSI] Format: [,,[,]] aic7xxx= [HW,SCSI] See Documentation/scsi/aic7xxx.txt. aic79xx= [HW,SCSI] See Documentation/scsi/aic79xx.txt. amijoy.map= [HW,JOY] Amiga joystick support Map of devices attached to JOY0DAT and JOY1DAT Format: , See also Documentation/kernel/input/joystick.txt analog.map= [HW,JOY] Analog joystick and gamepad support Specifies type or capabilities of an analog joystick connected to one of 16 gameports Format: ,,.. apc= [HW,SPARC] Power management functions (SPARCstation-4/5 + deriv.) Format: noidle Disable APC CPU standby support. SPARCstation-Fox does not play well with APC CPU idle - disable it if you have APC and your system crashes randomly. apic= [APIC,i386] Change the output verbosity whilst booting Format: { quiet (default) | verbose | debug } Change the amount of debugging information output when initialising the APIC and IO-APIC components. apm= [APM] Advanced Power Management See header of arch/i386/kernel/apm.c. applicom= [HW] Format: , arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards Format: ,, ataflop= [HW,M68k] atarimouse= [HW,MOUSE] Atari Mouse atascsi= [HW,SCSI] Atari SCSI atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, EzKey and similar keyboards atkbd.reset= [HW] Reset keyboard during initialization atkbd.set= [HW] Select keyboard code set Format: (2 = AT (default), 3 = PS/2) atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar keyboards atkbd.softraw= [HW] Choose between synthetic and real raw mode Format: (0 = real, 1 = synthetic (default)) atkbd.softrepeat= [HW] Use software keyboard repeat autotest [IA64] aztcd= [HW,CD] Aztech CD268 CDROM driver Format: ,0x79 (?) baycom_epp= [HW,AX25] Format: , baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem Format: , See header of drivers/net/hamradio/baycom_par.c. baycom_ser_fdx= [HW,AX25] BayCom Serial Port AX.25 Modem (Full Duplex Mode) Format: ,,[,] See header of drivers/net/hamradio/baycom_ser_fdx.c. baycom_ser_hdx= [HW,AX25] BayCom Serial Port AX.25 Modem (Half Duplex Mode) Format: ,, See header of drivers/net/hamradio/baycom_ser_hdx.c. blkmtd_device= [HW,MTD] blkmtd_erasesz= blkmtd_ro= blkmtd_bs= blkmtd_count= bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) bttv.radio= Most important insmod options are available as kernel args too. bttv.pll= See Documentation/video4linux/bttv/Insmod-options bttv.tuner= and Documentation/video4linux/bttv/CARDLIST BusLogic= [HW,SCSI] See drivers/scsi/BusLogic.c, comment before function BusLogic_ParseDriverOptions(). c101= [NET] Moxa C101 synchronous serial card cachesize= [BUGS=IA-32] Override level 2 CPU cache size detection. Sometimes CPU hardware bugs make them report the cache size incorrectly. The kernel will attempt work arounds to fix known problems, but for some CPUs it is not possible to determine what the correct size should be. This option provides an override for these situations. cdu31a= [HW,CD] Format: ,[,PAS] See header of drivers/cdrom/cdu31a.c. chandev= [HW,NET] Generic channel device initialisation checkreqprot [SELINUX] Set initial checkreqprot flag value. Format: { "0" | "1" } See security/selinux/Kconfig help text. 0 -- check protection applied by kernel (includes any implied execute protection). 1 -- check protection requested by application. Default value is set via a kernel config option. Value can be changed at runtime via /selinux/checkreqprot. clock= [BUGS=IA-32, HW] gettimeofday clocksource override. [Deprecated] Forces specified clocksource (if available) to be used when calculating gettimeofday(). If specified clocksource is not available, it defaults to PIT. Format: { pit | tsc | cyclone | pmtmr } disable_8254_timer enable_8254_timer [IA32/X86_64] Disable/Enable interrupt 0 timer routing over the 8254 in addition to over the IO-APIC. The kernel tries to set a sensible default. hpet= [IA-32,HPET] option to disable HPET and use PIT. Format: disable cm206= [HW,CD] Format: { auto | [,][] } com20020= [HW,NET] ARCnet - COM20020 chipset Format: [,[,[,[,[,]]]]] com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) Format: [,] com90xx= [HW,NET] ARCnet - COM90xx chipset (memory-mapped buffers) Format: [,[,]] condev= [HW,S390] console device conmode= console= [KNL] Output console device and options. tty Use the virtual console device . ttyS[,options] ttyUSB0[,options] Use the specified serial port. The options are of the form "bbbbpnf", where "bbbb" is the baud rate, "p" is parity ("n", "o", or "e"), "n" is number of bits, and "f" is flow control ("r" for RTS or omit it). Default is "9600n8". See Documentation/serial-console.txt for more information. See Documentation/networking/netconsole.txt for an alternative. uart,io,[,options] uart,mmio,[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address, switching to the matching ttyS device later. The options are the same as for ttyS, above. cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver Format: ,,,[,] cpia_pp= [HW,PPT] Format: { parport | auto | none } crashkernel=nn[KMG]@ss[KMG] [KNL] Reserve a chunk of physical memory to hold a kernel to switch to with kexec on panic. cs4232= [HW,OSS] Format: ,,,,, cs89x0_dma= [HW,NET] Format: cs89x0_media= [HW,NET] Format: { rj45 | aui | bnc } cyclades= [HW,SERIAL] Cyclades multi-serial port adapter. dasd= [HW,NET] See header of drivers/s390/block/dasd_devmap.c. db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port (one device per port) Format: , See also Documentation/input/joystick-parport.txt debug [KNL] Enable kernel debugging (events log level). debug_locks_verbose= [KNL] verbose self-tests Format=<0|1> Print debugging info while doing the locking API self-tests. We default to 0 (no extra messages), setting it to 1 will print _a lot_ more information - normally only useful to kernel developers. decnet= [HW,NET] Format: [,] See also Documentation/networking/decnet.txt. dhash_entries= [KNL] Set number of hash buckets for dentry cache. digi= [HW,SERIAL] IO parameters + enable/disable command. digiepca= [HW,SERIAL] See drivers/char/README.epca and Documentation/digiepca.txt. dmascc= [HW,AX25,SERIAL] AX.25 Z80SCC driver with DMA support available. Format: [,[,..]] dmasound= [HW,OSS] Sound subsystem buffers dscc4.setup= [NET] dtc3181e= [HW,SCSI] earlyprintk= [IA-32,X86-64] earlyprintk=vga earlyprintk=serial[,ttySn[,baudrate]] Append ",keep" to not disable it when the real console takes over. Only vga or serial at a time, not both. Currently only ttyS0 and ttyS1 are supported. Interaction with the standard serial driver is not very good. The VGA output is eventually overwritten by the real console. eata= [HW,SCSI] ec_intr= [HW,ACPI] ACPI Embedded Controller interrupt mode Format: 0: polling mode non-0: interrupt mode (default) eda= [HW,PS2] edb= [HW,PS2] edd= [EDD] Format: {"of[f]" | "sk[ipmbr]"} See comment in arch/i386/boot/edd.S eicon= [HW,ISDN] Format: ,, eisa_irq_edge= [PARISC,HW] See header of drivers/parisc/eisa.c. elanfreq= [IA-32] See comment before function elanfreq_setup() in arch/i386/kernel/cpu/cpufreq/elanfreq.c. elevator= [IOSCHED] Format: {"anticipatory" | "cfq" | "deadline" | "noop"} See Documentation/block/as-iosched.txt and Documentation/block/deadline-iosched.txt for details. elfcorehdr= [IA-32, X86_64] Specifies physical address of start of kernel core image elf header. Generally kexec loader will pass this option to capture kernel. See Documentation/kdump/kdump.txt for details. enforcing [SELINUX] Set initial enforcing status. Format: {"0" | "1"} See security/selinux/Kconfig help text. 0 -- permissive (log only, no denials). 1 -- enforcing (deny and log). Default value is 0. Value can be changed at runtime via /selinux/enforce. es1371= [HW,OSS] Format: ,[,[]] See also header of sound/oss/es1371.c. ether= [HW,NET] Ethernet cards parameters This option is obsoleted by the "netdev=" option, which has equivalent usage. See its documentation for details. eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog. Format: [,] fd_mcs= [HW,SCSI] See header of drivers/scsi/fd_mcs.c. fdomain= [HW,SCSI] See header of drivers/scsi/fdomain.c. floppy= [HW] See Documentation/floppy.txt. gamecon.map[2|3]= [HW,JOY] Multisystem joystick and NES/SNES/PSX pad support via parallel port (up to 5 devices per port) Format: ,,,,, See also Documentation/input/joystick-parport.txt gamma= [HW,DRM] gdth= [HW,SCSI] See header of drivers/scsi/gdth.c. gpt [EFI] Forces disk with valid GPT signature but invalid Protective MBR to be treated as GPT. gscd= [HW,CD] Format: gvp11= [HW,SCSI] hashdist= [KNL,NUMA] Large hashes allocated during boot are distributed across NUMA nodes. Defaults on for IA-64, off otherwise. Format: 0 | 1 (for off | on) hcl= [IA-64] SGI's Hardware Graph compatibility layer hd= [EIDE] (E)IDE hard drive subsystem geometry Format: ,, hd?= [HW] (E)IDE subsystem hd?lun= See Documentation/ide.txt. highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact size of . This works even on boxes that have no highmem otherwise. This also works to reduce highmem size on bigger boxes. hisax= [HW,ISDN] See Documentation/isdn/README.HiSax. hugepages= [HW,IA-32,IA-64] Maximal number of HugeTLB pages. noirqbalance [IA-32,SMP,KNL] Disable kernel irq balancing i8042.direct [HW] Put keyboard port into non-translated mode i8042.dumbkbd [HW] Pretend that controller can only read data from keyboard and cannot control its state (Don't attempt to blink the leds) i8042.noaux [HW] Don't check for auxiliary (== mouse) port i8042.nokbd [HW] Don't check/create keyboard port i8042.nomux [HW] Don't check presence of an active multiplexing controller i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX controllers i8042.panicblink= [HW] Frequency with which keyboard LEDs should blink when kernel panics (default is 0.5 sec) i8042.reset [HW] Reset the controller during init and cleanup i8042.unlock [HW] Unlock (ignore) the keylock i810= [HW,DRM] i8k.ignore_dmi [HW] Continue probing hardware even if DMI data indicates that the driver is running on unsupported hardware. i8k.force [HW] Activate i8k driver even if SMM BIOS signature does not match list of supported models. i8k.power_status [HW] Report power status in /proc/i8k (disabled by default) i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN capability is set. ibmmcascsi= [HW,MCA,SCSI] IBM MicroChannel SCSI adapter See Documentation/mca.txt. icn= [HW,ISDN] Format: [,[,[,]]] ide= [HW] (E)IDE subsystem Format: ide=nodma or ide=doubler or ide=reverse See Documentation/ide.txt. ide?= [HW] (E)IDE subsystem Format: ide?=noprobe or chipset specific parameters. See Documentation/ide.txt. idebus= [HW] (E)IDE subsystem - VLB/PCI bus speed See Documentation/ide.txt. idle= [HW] Format: idle=poll or idle=halt ihash_entries= [KNL] Set number of hash buckets for inode cache. in2000= [HW,SCSI] See header of drivers/scsi/in2000.c. init= [KNL] Format: Run specified binary instead of /sbin/init as init process. initcall_debug [KNL] Trace initcalls as they are executed. Useful for working out where the kernel is dying during startup. initrd= [BOOT] Specify the location of the initial ramdisk inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver Format: combined_mode= [HW] control which driver uses IDE ports in combined mode: legacy IDE driver, libata, or both (in the libata case, libata.atapi_enabled=1 may be useful as well). Note that using the ide or libata options may affect your device naming (e.g. by changing hdc to sdb). Format: combined (default), ide, or libata inttest= [IA64] io7= [HW] IO7 for Marvel based alpha systems See comment before marvel_specify_io7 in arch/alpha/kernel/core_marvel.c. ip= [IP_PNP] See Documentation/nfsroot.txt. ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards See comment before ip2_setup() in drivers/char/ip2.c. ips= [HW,SCSI] Adaptec / IBM ServeRAID controller See header of drivers/scsi/ips.c. ports= [IP_VS_FTP] IPVS ftp helper module Default is 21. Up to 8 (IP_VS_APP_MAX_PORTS) ports may be specified. Format: ,.... irqfixup [HW] When an interrupt is not handled search all handlers for it. Intended to get systems with badly broken firmware running. irqpoll [HW] When an interrupt is not handled search all handlers for it. Also check all handlers each timer interrupt. Intended to get systems with badly broken firmware running. isapnp= [ISAPNP] Format: ,,, isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. Format: ,..., This option can be used to specify one or more CPUs to isolate from the general SMP balancing and scheduling algorithms. The only way to move a process onto or off an "isolated" CPU is via the CPU affinity syscalls. begins at 0 and the maximum value is "number of CPUs in system - 1". This option is the preferred way to isolate CPUs. The alternative -- manually setting the CPU mask of all tasks in the system -- can cause problems and suboptimal load balancer performance. isp16= [HW,CD] Format: ,,, iucv= [HW,NET] js= [HW,JOY] Analog joystick See Documentation/input/joystick.txt. keepinitrd [HW,ARM] kstack=N [IA-32,X86-64] Print N words from the kernel stack in oops dumps. l2cr= [PPC] lapic [IA-32,APIC] Enable the local APIC even if BIOS disabled it. lasi= [HW,SCSI] PARISC LASI driver for the 53c700 chip Format: addr:,irq: llsc*= [IA64] See function print_params() in arch/ia64/sn/kernel/llsc4.c. load_ramdisk= [RAM] List of ramdisks to load from floppy See Documentation/ramdisk.txt. lockd.nlm_grace_period=P [NFS] Assign grace period. Format: lockd.nlm_tcpport=N [NFS] Assign TCP port. Format: lockd.nlm_timeout=T [NFS] Assign timeout value. Format: lockd.nlm_udpport=M [NFS] Assign UDP port. Format: logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver Format: loglevel= All Kernel Messages with a loglevel smaller than the console loglevel will be printed to the console. It can also be changed with klogd or other programs. The loglevels are defined as follows: 0 (KERN_EMERG) system is unusable 1 (KERN_ALERT) action must be taken immediately 2 (KERN_CRIT) critical conditions 3 (KERN_ERR) error conditions 4 (KERN_WARNING) warning conditions 5 (KERN_NOTICE) normal but significant condition 6 (KERN_INFO) informational 7 (KERN_DEBUG) debug-level messages log_buf_len=n Sets the size of the printk ring buffer, in bytes. Format: { n | nk | nM } n must be a power of two. The default size is set in the kernel config file. lp=0 [LP] Specify parallel ports to use, e.g, lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses lp=reset first parallel port). 'lp=0' disables the lp=auto printer driver. 'lp=reset' (which can be specified in addition to the ports) causes attached printers to be reset. Using lp=port1,port2,... specifies the parallel ports to associate lp devices with, starting with lp0. A port specification may be 'none' to skip that lp device, or a parport name such as 'parport0'. Specifying 'lp=auto' instead of a port specification list means that device IDs from each port should be examined, to see if an IEEE 1284-compliant printer is attached; if so, the driver will manage that printer. See also header of drivers/char/lp.c. lpj=n [KNL] Sets loops_per_jiffy to given constant, thus avoiding time-consuming boot-time autodetection (up to 250 ms per CPU). 0 enables autodetection (default). To determine the correct value for your kernel, boot with normal autodetection and see what value is printed. Note that on SMP systems the preset will be applied to all CPUs, which is likely to cause problems if your CPUs need significantly divergent settings. An incorrect value will cause delays in the kernel to be wrong, leading to unpredictable I/O errors and other breakage. Although unlikely, in the extreme case this might damage your hardware. ltpc= [NET] Format: ,, mac5380= [HW,SCSI] Format: ,,,, mac53c9x= [HW,SCSI] Format: ,,,,,,, machvec= [IA64] Force the use of a particular machine-vector (machvec) in a generic kernel. Example: machvec=hpzx1_swiotlb max_loop= [LOOP] Maximum number of loopback devices that can be mounted Format: <1-256> maxcpus= [SMP] Maximum number of processors that an SMP kernel should make use of max_addr=[KMG] [KNL,BOOT,ia64] All physical memory greater than or equal to this physical address is ignored. max_luns= [SCSI] Maximum number of LUNs to probe. Should be between 1 and 2^32-1. max_report_luns= [SCSI] Maximum number of LUNs received. Should be between 1 and 16384. mca-pentium [BUGS=IA-32] mcatest= [IA-64] mcd= [HW,CD] Format: ,, mcdx= [HW,CD] mce [IA-32] Machine Check Exception md= [HW] RAID subsystems devices and level See Documentation/md.txt. mdacon= [MDA] Format: , Specifies range of consoles to be captured by the MDA. mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory Amount of memory to be used when the kernel is not able to see the whole system memory or for test. [IA-32] Use together with memmap= to avoid physical address space collisions. Without memmap= PCI devices could be placed at addresses belonging to unused RAM. mem=nopentium [BUGS=IA-32] Disable usage of 4MB pages for kernel memory. memmap=exactmap [KNL,IA-32,X86_64] Enable setting of an exact E820 memory map, as specified by the user. Such memmap=exactmap lines can be constructed based on BIOS output or other requirements. See the memmap=nn@ss option description. memmap=nn[KMG]@ss[KMG] [KNL] Force usage of a specific region of memory Region of memory to be used, from ss to ss+nn. memmap=nn[KMG]#ss[KMG] [KNL,ACPI] Mark specific memory as ACPI data. Region of memory to be used, from ss to ss+nn. memmap=nn[KMG]$ss[KMG] [KNL,ACPI] Mark specific memory as reserved. Region of memory to be used, from ss to ss+nn. meye.*= [HW] Set MotionEye Camera parameters See Documentation/video4linux/meye.txt. mga= [HW,DRM] migration_cost= [KNL,SMP] debug: override scheduler migration costs Format: ,,... This debugging option can be used to override the default scheduler migration cost matrix. The numbers are indexed by 'CPU domain distance'. E.g. migration_cost=1000,2000,3000 on an SMT NUMA box will set up an intra-core migration cost of 1 msec, an inter-core migration cost of 2 msecs, and an inter-node migration cost of 3 msecs. WARNING: using the wrong values here can break scheduler performance, so it's only for scheduler development purposes, not production environments. migration_debug= [KNL,SMP] migration cost auto-detect verbosity Format=<0|1|2> If a system's migration matrix reported at bootup seems erroneous then this option can be used to increase verbosity of the detection process. We default to 0 (no extra messages), 1 will print some more information, and 2 will be really verbose (probably only useful if you also have a serial console attached to the system). migration_factor= [KNL,SMP] multiply/divide migration costs by a factor Format= This debug option can be used to proportionally increase or decrease the auto-detected migration costs for all entries of the migration matrix. E.g. migration_factor=150 will increase migration costs by 50%. (and thus the scheduler will be less eager migrating cache-hot tasks) migration_factor=80 will decrease migration costs by 20%. (thus the scheduler will be more eager to migrate tasks) WARNING: using the wrong values here can break scheduler performance, so it's only for scheduler development purposes, not production environments. mousedev.tap_time= [MOUSE] Maximum time between finger touching and leaving touchpad surface for touch to be considered a tap and be reported as a left button click (for touchpads working in absolute mode only). Format: mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices reporting absolute coordinates, such as tablets mousedev.yres= [MOUSE] Vertical screen resolution, used for devices reporting absolute coordinates, such as tablets mpu401= [HW,OSS] Format: , MTD_Partition= [MTD] Format: ,,, MTD_Region= [MTD] Format: ,[,,,,] mtdparts= [MTD] See drivers/mtd/cmdline.c. mtouchusb.raw_coordinates= [HW] Make the MicroTouch USB driver use raw coordinates ('y', default) or cooked coordinates ('n') n2= [NET] SDL Inc. RISCom/N2 synchronous serial card NCR_D700= [HW,SCSI] See header of drivers/scsi/NCR_D700.c. ncr5380= [HW,SCSI] ncr53c400= [HW,SCSI] ncr53c400a= [HW,SCSI] ncr53c406a= [HW,SCSI] ncr53c8xx= [HW,SCSI] netdev= [NET] Network devices parameters Format: ,,,, Note that mem_start is often overloaded to mean something different and driver-specific. This usage is only documented in each driver source file if at all. nfsaddrs= [NFS] See Documentation/nfsroot.txt. nfsroot= [NFS] nfs root filesystem for disk-less boxes. See Documentation/nfsroot.txt. nfs.callback_tcpport= [NFS] set the TCP port on which the NFSv4 callback channel should listen. nfs.idmap_cache_timeout= [NFS] set the maximum lifetime for idmapper cache entries. nmi_watchdog= [KNL,BUGS=IA-32] Debugging features for SMP kernels no387 [BUGS=IA-32] Tells the kernel to use the 387 maths emulation library even if a 387 maths coprocessor is present. noalign [KNL,ARM] noapic [SMP,APIC] Tells the kernel to not make use of any IOAPICs that may be present in the system. noasync [HW,M68K] Disables async and sync negotiation for all devices. nobats [PPC] Do not use BATs for mapping kernel lowmem on "Classic" PPC cores. nocache [ARM] nodelayacct [KNL] Disable per-task delay accounting nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects. noexec [IA-64] noexec [IA-32,X86-64] noexec=on: enable non-executable mappings (default) noexec=off: disable nn-executable mappings nofxsr [BUGS=IA-32] Disables x86 floating point extended register save and restore. The kernel will only save legacy floating-point registers on task switch. nohlt [BUGS=ARM] no-hlt [BUGS=IA-32] Tells the kernel that the hlt instruction doesn't work correctly and not to use it. nohalt [IA-64] Tells the kernel not to use the power saving function PAL_HALT_LIGHT when idle. This increases power-consumption. On the positive side, it reduces interrupt wake-up latency, which may improve performance in certain environments such as networked servers or real-time systems. noirqdebug [IA-32] Disables the code which attempts to detect and disable unhandled interrupt sources. noisapnp [ISAPNP] Disables ISA PnP code. noinitrd [RAM] Tells the kernel not to load any configured initial RAM disk. nointroute [IA-64] nolapic [IA-32,APIC] Do not enable or use the local APIC. noltlbs [PPC] Do not use large page/tlb entries for kernel lowmem mapping on PPC40x. nomca [IA-64] Disable machine check abort handling nomce [IA-32] Machine Check Exception noresidual [PPC] Don't use residual data on PReP machines. noresume [SWSUSP] Disables resume and restores original swap space. no-scroll [VGA] Disables scrollback. This is required for the Braillex ib80-piezo Braille reader made by F.H. Papenmeier (Germany). nosbagart [IA-64] nosep [BUGS=IA-32] Disables x86 SYSENTER/SYSEXIT support. nosmp [SMP] Tells an SMP kernel to act as a UP kernel. nosync [HW,M68K] Disables sync negotiation for all devices. notsc [BUGS=IA-32] Disable Time Stamp Counter nousb [USB] Disable the USB subsystem nowb [ARM] nr_uarts= [SERIAL] maximum number of UARTs to be registered. opl3= [HW,OSS] Format: opl3sa2= [HW,OSS] Format: ,,,,,,,[,, osst= [HW,SCSI] SCSI Tape Driver Format: , See also Documentation/scsi/st.txt. panic= [KNL] Kernel behaviour on panic Format: parkbd.port= [HW] Parallel port number the keyboard adapter is connected to, default is 0. Format: parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 0 for XT, 1 for AT (default is AT). Format: parport= [HW,PPT] Specify parallel ports. 0 disables. Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } Use 'auto' to force the driver to use any IRQ/DMA settings detected (the default is to ignore detected IRQ/DMA settings because of possible conflicts). You can specify the base address, IRQ, and DMA settings; IRQ and DMA should be numbers, or 'auto' (for using detected settings on that particular port), or 'nofifo' (to avoid using a FIFO even if it is detected). Parallel ports are assigned in the order they are specified on the command line, starting with parport0. parport_init_mode= [HW,PPT] Configure VIA parallel port to operate in a specific mode. This is necessary on Pegasos computer where firmware has no options for setting up parallel port mode and sets it to spp. Currently this function knows 686a and 8231 chips. Format: [spp|ps2|epp|ecp|ecpepp] pas2= [HW,OSS] Format: ,,,,,,, pas16= [HW,SCSI] See header of drivers/scsi/pas16.c. pause_on_oops= Halt all CPUs after the first oops has been printed for the specified number of seconds. This is to be used if your oopses keep scrolling off the screen. pcbit= [HW,ISDN] pcd. [PARIDE] See header of drivers/block/paride/pcd.c. See also Documentation/paride.txt. pci=option[,option...] [PCI] various PCI subsystem options: off [IA-32] don't probe for the PCI bus bios [IA-32] force use of PCI BIOS, don't access the hardware directly. Use this if your machine has a non-standard PCI host bridge. nobios [IA-32] disallow use of PCI BIOS, only direct hardware access methods are allowed. Use this if you experience crashes upon bootup and you suspect they are caused by the BIOS. conf1 [IA-32] Force use of PCI Configuration Mechanism 1. conf2 [IA-32] Force use of PCI Configuration Mechanism 2. nommconf [IA-32,X86_64] Disable use of MMCONFIG for PCI Configuration nomsi [MSI] If the PCI_MSI kernel config parameter is enabled, this kernel boot option can be used to disable the use of MSI interrupts system-wide. nosort [IA-32] Don't sort PCI devices according to order given by the PCI BIOS. This sorting is done to get a device order compatible with older kernels. biosirq [IA-32] Use PCI BIOS calls to get the interrupt routing table. These calls are known to be buggy on several machines and they hang the machine when used, but on other computers it's the only way to get the interrupt routing table. Try this option if the kernel is unable to allocate IRQs or discover secondary PCI buses on your motherboard. rom [IA-32] Assign address space to expansion ROMs. Use with caution as certain devices share address decoders between ROMs and other resources. irqmask=0xMMMM [IA-32] Set a bit mask of IRQs allowed to be assigned automatically to PCI devices. You can make the kernel exclude IRQs of your ISA cards this way. pirqaddr=0xAAAAA [IA-32] Specify the physical address of the PIRQ table (normally generated by the BIOS) if it is outside the F0000h-100000h range. lastbus=N [IA-32] Scan all buses thru bus #N. Can be useful if the kernel is unable to find your secondary buses and you want to tell it explicitly which ones they are. assign-busses [IA-32] Always assign all PCI bus numbers ourselves, overriding whatever the firmware may have done. usepirqmask [IA-32] Honor the possible IRQ mask stored in the BIOS $PIR table. This is needed on some systems with broken BIOSes, notably some HP Pavilion N5400 and Omnibook XE3 notebooks. This will have no effect if ACPI IRQ routing is enabled. noacpi [IA-32] Do not use ACPI for IRQ routing or for PCI scanning. routeirq Do IRQ routing for all PCI devices. This is normally done in pci_enable_device(), so this option is a temporary workaround for broken drivers that don't call it. firmware [ARM] Do not re-enumerate the bus but instead just use the configuration from the bootloader. This is currently used on IXP2000 systems where the bus has to be configured a certain way for adjunct CPUs. noearly [X86] Don't do any early type 1 scanning. This might help on some broken boards which machine check when some devices' config space is read. But various workarounds are disabled and some IOMMU drivers will not work. bfsort Sort PCI devices into breadth-first order. This sorting is done to get a device order compatible with older (<= 2.4) kernels. nobfsort Don't sort PCI devices into breadth-first order. pcmv= [HW,PCMCIA] BadgePAD 4 pd. [PARIDE] See Documentation/paride.txt. pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at boot time. Format: { 0 | 1 } See arch/parisc/kernel/pdc_chassis.c pf. [PARIDE] See Documentation/paride.txt. pg. [PARIDE] See Documentation/paride.txt. pirq= [SMP,APIC] Manual mp-table setup See Documentation/i386/IO-APIC.txt. plip= [PPT,NET] Parallel port network link Format: { parport | timid | 0 } See also Documentation/parport.txt. pnpacpi= [ACPI] { off } pnpbios= [ISAPNP] { on | off | curr | res | no-curr | no-res } pnp_reserve_irq= [ISAPNP] Exclude IRQs for the autoconfiguration pnp_reserve_dma= [ISAPNP] Exclude DMAs for the autoconfiguration pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration Ranges are in pairs (I/O port base and size). pnp_reserve_mem= [ISAPNP] Exclude memory regions for the autoconfiguration. Ranges are in pairs (memory base and size). profile= [KNL] Enable kernel profiling via /proc/profile Format: [schedule,] Param: "schedule" - profile schedule points. Param: - step/bucket size as a power of 2 for statistical time based profiling. processor.max_cstate= [HW,ACPI] Limit processor to maximum C-state max_cstate=9 overrides any DMI blacklist limit. processor.nocst [HW,ACPI] Ignore the _CST method to determine C-states, instead using the legacy FADT method prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk before loading. See Documentation/ramdisk.txt. psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to probe for; one of (bare|imps|exps|lifebook|any). psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports per second. psmouse.resetafter= [HW,MOUSE] Try to reset the device after so many bad packets (0 = never). psmouse.resolution= [HW,MOUSE] Set desired mouse resolution, in dpi. psmouse.smartscroll= [HW,MOUSE] Controls Logitech smartscroll autorepeat. 0 = disabled, 1 = enabled (default). pss= [HW,OSS] Personal Sound System (ECHO ESC614) Format: ,,,,, pt. [PARIDE] See Documentation/paride.txt. quiet [KNL] Disable most log messages r128= [HW,DRM] raid= [HW,RAID] See Documentation/md.txt. ramdisk= [RAM] Sizes of RAM disks in kilobytes [deprecated] See Documentation/ramdisk.txt. ramdisk_blocksize= [RAM] See Documentation/ramdisk.txt. ramdisk_size= [RAM] Sizes of RAM disks in kilobytes New name for the ramdisk parameter. See Documentation/ramdisk.txt. rcu.blimit= [KNL,BOOT] Set maximum number of finished RCU callbacks to process in one batch. rcu.qhimark= [KNL,BOOT] Set threshold of queued RCU callbacks over which batch limiting is disabled. rcu.qlowmark= [KNL,BOOT] Set threshold of queued RCU callbacks below which batch limiting is re-enabled. rdinit= [KNL] Format: Run specified binary instead of /init from the ramdisk, used for early userspace startup. See initrd. reboot= [BUGS=IA-32,BUGS=ARM,BUGS=IA-64] Rebooting mode Format: [,[,...]] See arch/*/kernel/reboot.c or arch/*/kernel/process.c reserve= [KNL,BUGS] Force the kernel to ignore some iomem area reservetop= [IA-32] Format: nn[KMG] Reserves a hole at the top of the kernel virtual address space. reset_devices [KNL] Force drivers to reset the underlying device during initialization. resume= [SWSUSP] Specify the partition device for software suspend rhash_entries= [KNL,NET] Set number of hash buckets for route cache riscom8= [HW,SERIAL] Format: [,[,...]] ro [KNL] Mount root device read-only on boot root= [KNL] Root filesystem rootdelay= [KNL] Delay (in seconds) to pause before attempting to mount the root filesystem rootflags= [KNL] Set root filesystem mount option string rootfstype= [KNL] Set root filesystem type rw [KNL] Mount root device read-write on boot S [KNL] Run init in single mode sa1100ir [NET] See drivers/net/irda/sa1100_ir.c. sb= [HW,OSS] Format: ,,, sbni= [NET] Granch SBNI12 leased line adapter sbpcd= [HW,CD] Soundblaster CD adapter Format: , See a comment before function sbpcd_setup() in drivers/cdrom/sbpcd.c. sc1200wdt= [HW,WDT] SC1200 WDT (watchdog) driver Format: [,[,]] scsi_debug_*= [SCSI] See drivers/scsi/scsi_debug.c. scsi_default_dev_flags= [SCSI] SCSI default device flags Format: scsi_dev_flags= [SCSI] Black/white list entry for vendor and model Format: :: (flags are integer value) scsi_logging= [SCSI] scsi_mod.scan= [SCSI] sync (default) scans SCSI busses as they are discovered. async scans them in kernel threads, allowing boot to proceed. none ignores them, expecting user space to do the scan. selinux [SELINUX] Disable or enable SELinux at boot time. Format: { "0" | "1" } See security/selinux/Kconfig help text. 0 -- disable. 1 -- enable. Default value is set via kernel config option. If enabled at boot time, /selinux/disable can be used later to disable prior to initial policy load. selinux_compat_net = [SELINUX] Set initial selinux_compat_net flag value. Format: { "0" | "1" } 0 -- use new secmark-based packet controls 1 -- use legacy packet controls Default value is 0 (preferred). Value can be changed at runtime via /selinux/compat_net. serialnumber [BUGS=IA-32] sg_def_reserved_size= [SCSI] shapers= [NET] Maximal number of shapers. sim710= [SCSI,HW] See header of drivers/scsi/sim710.c. simeth= [IA-64] simscsi= sjcd= [HW,CD] Format: ,, See header of drivers/cdrom/sjcd.c. slram= [HW,MTD] smart2= [HW] Format: [,[,...,]] snd-ad1816a= [HW,ALSA] snd-ad1848= [HW,ALSA] snd-ali5451= [HW,ALSA] snd-als100= [HW,ALSA] snd-als4000= [HW,ALSA] snd-azt2320= [HW,ALSA] snd-cmi8330= [HW,ALSA] snd-cmipci= [HW,ALSA] snd-cs4231= [HW,ALSA] snd-cs4232= [HW,ALSA] snd-cs4236= [HW,ALSA] snd-cs4281= [HW,ALSA] snd-cs46xx= [HW,ALSA] snd-dt019x= [HW,ALSA] snd-dummy= [HW,ALSA] snd-emu10k1= [HW,ALSA] snd-ens1370= [HW,ALSA] snd-ens1371= [HW,ALSA] snd-es968= [HW,ALSA] snd-es1688= [HW,ALSA] snd-es18xx= [HW,ALSA] snd-es1938= [HW,ALSA] snd-es1968= [HW,ALSA] snd-fm801= [HW,ALSA] snd-gusclassic= [HW,ALSA] snd-gusextreme= [HW,ALSA] snd-gusmax= [HW,ALSA] snd-hdsp= [HW,ALSA] snd-ice1712= [HW,ALSA] snd-intel8x0= [HW,ALSA] snd-interwave= [HW,ALSA] snd-interwave-stb= [HW,ALSA] snd-korg1212= [HW,ALSA] snd-maestro3= [HW,ALSA] snd-mpu401= [HW,ALSA] snd-mtpav= [HW,ALSA] snd-nm256= [HW,ALSA] snd-opl3sa2= [HW,ALSA] snd-opti92x-ad1848= [HW,ALSA] snd-opti92x-cs4231= [HW,ALSA] snd-opti93x= [HW,ALSA] snd-pmac= [HW,ALSA] snd-rme32= [HW,ALSA] snd-rme96= [HW,ALSA] snd-rme9652= [HW,ALSA] snd-sb8= [HW,ALSA] snd-sb16= [HW,ALSA] snd-sbawe= [HW,ALSA] snd-serial= [HW,ALSA] snd-sgalaxy= [HW,ALSA] snd-sonicvibes= [HW,ALSA] snd-sun-amd7930= [HW,ALSA] snd-sun-cs4231= [HW,ALSA] snd-trident= [HW,ALSA] snd-usb-audio= [HW,ALSA,USB] snd-via82xx= [HW,ALSA] snd-virmidi= [HW,ALSA] snd-wavefront= [HW,ALSA] snd-ymfpci= [HW,ALSA] sonycd535= [HW,CD] Format: [,] sonypi.*= [HW] Sony Programmable I/O Control Device driver See Documentation/sonypi.txt specialix= [HW,SERIAL] Specialix multi-serial port adapter See Documentation/specialix.txt. spia_io_base= [HW,MTD] spia_fio_base= spia_pedr= spia_peddr= sscape= [HW,OSS] Format: ,,,, st= [HW,SCSI] SCSI tape parameters (buffers, etc.) See Documentation/scsi/st.txt. st0x= [HW,SCSI] See header of drivers/scsi/seagate.c. sti= [PARISC,HW] Format: Set the STI (builtin display/keyboard on the HP-PARISC machines) console (graphic card) which should be used as the initial boot-console. See also comment in drivers/video/console/sticore.c. sti_font= [HW] See comment in drivers/video/console/sticore.c. stifb= [HW] Format: bpp:[:[:...]] swiotlb= [IA-64] Number of I/O TLB slabs switches= [HW,M68k] sym53c416= [HW,SCSI] See header of drivers/scsi/sym53c416.c. t128= [HW,SCSI] See header of drivers/scsi/t128.c. tdfx= [HW,DRM] thash_entries= [KNL,NET] Set number of hash buckets for TCP connection time Show timing data prefixed to each printk message line clocksource= [GENERIC_TIME] Override the default clocksource Override the default clocksource and use the clocksource with the name specified. tipar.timeout= [HW,PPT] Set communications timeout in tenths of a second (default 15). tipar.delay= [HW,PPT] Set inter-bit delay in microseconds (default 10). tmc8xx= [HW,SCSI] See header of drivers/scsi/seagate.c. tmscsim= [HW,SCSI] See comment before function dc390_setup() in drivers/scsi/tmscsim.c. tp720= [HW,PS2] trix= [HW,OSS] MediaTrix AudioTrix Pro Format: ,,,,,,,, tsdev.xres= [TS] Horizontal screen resolution. tsdev.yres= [TS] Vertical screen resolution. turbografx.map[2|3]= [HW,JOY] TurboGraFX parallel port interface Format: ,,,,,,, See also Documentation/input/joystick-parport.txt u14-34f= [HW,SCSI] UltraStor 14F/34F SCSI host adapter See header of drivers/scsi/u14-34f.c. uart401= [HW,OSS] Format: , uart6850= [HW,OSS] Format: , usbhid.mousepoll= [USBHID] The interval which mice are to be polled at. vdso= [IA-32] vdso=1: enable VDSO (default) vdso=0: disable VDSO mapping video= [FB] Frame buffer configuration See Documentation/fb/modedb.txt. vga= [BOOT,IA-32] Select a particular video mode See Documentation/i386/boot.txt and Documentation/svga.txt. Use vga=ask for menu. This is actually a boot loader parameter; the value is passed to the kernel using a special protocol. vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact size of . This can be used to increase the minimum size (128MB on x86). It can also be used to decrease the size and leave more room for directly mapped kernel RAM. vmhalt= [KNL,S390] Perform z/VM CP command after system halt. Format: vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. Format: vmpoff= [KNL,S390] Perform z/VM CP command after power off. Format: waveartist= [HW,OSS] Format: ,,, wd33c93= [HW,SCSI] See header of drivers/scsi/wd33c93.c. wd7000= [HW,SCSI] See header of drivers/scsi/wd7000.c. wdt= [WDT] Watchdog See Documentation/watchdog/watchdog.txt. xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks. xd_geo= See header of drivers/block/xd.c. xirc2ps_cs= [NET,PCMCIA] Format: ,,,,,[,[,[,]]] norandmaps Don't use address space randomization Equivalent to echo 0 > /proc/sys/kernel/randomize_va_space ______________________________________________________________________ TODO: Add documentation for ALSA options. Add more DRM drivers.